would need some custom pistons designing and making for one thing as the 16v head has combustion chambers in it where as the 8v g40 head is flat with combustion chambers in the pistons.
Otherwise you'll also need custom inlet and exhaust manifolds, possilble plugging of one or two oil or waterways. I'm fairly sure all the head bolt holes and most of the oil and waterways match up but this is by no means a bolt-on job. Would be interesting to see though.
